1. Field of the Invention
This invention relates to novel polypeptides, DNAs that code for the same and method of preparing said polypeptides and DNAs. More particularly, it relates to IgG.sub.1 inducing factor, which is one of the T-cell humoral factors playing an important role in the regulation and control of immune response in living bodies, to DNAs that code for the same, and to a method for preparing said factor and DNAs.
It is well known that T cells and B cells participate in the immunological reaction system in living bodies.
B cells differentiate from hematopoietic stem cells into mature B cells having, on the surface of cell membrane, IgM and IgD as antigen receptor. The mature B cells thus formed then propagate by stimulation of specific antigens, eventually differentiating into anti-body producing cells. It is known that this propagation of B cells caused by antigen stimulation requires the action of T-cell-derived humoral factors; Studies are actively under way in many laboratories over the world on these humoral factors by using various cell lines, hybridomas and clones derived from T cells.
These T-cell-derived humoral factors might be divided into the following three groups in terms of activity: the first group containing factors which, by acting before and after stimulation, induces resting B cells into growth cycle or promotes differentiation including class switch recombination; the second group containing factors which serve to maintain such growth of B cells; and the third group containing factors which act upon the B cells propagated by antigen stimulation and by the action of the first and second group factors, forcing them to secrete antibodies.
Cloning the genes of these factors, allowing each gene to establish itself, and studying them individually would provide a powerful means to characterize the physiological functions of each factor and to effectively utilize them as medicines.
2. Description of the Prior Art
The presence of mouse IgG.sub.1 inducing factor has already been suggested, but none of known techniques has so far been successful in isolating this factor. For example, when a cells capable of producing said factor is grown, the resultant culture medium contains much impurities and only an extremely small amount of said factor, making its isolation practically impossible. In the technique to isolate mRNA from the cells producing said factor, thereby cloning the objective gene, this cloning operation is extremely difficult because of the minute amount of the objective mRNA and the presence of many other types of mRNA. Thus nothing is known about the structure of said IgG.sub.1 inducing factor, not to mention the DNA that codes for this factor.